In spite of its woefully stupid name, the Cadillac Converj was the hit of the 2009 Detroit auto show. Beyond the buzz generated simply from its wedgy, mini-Gallardo looks, the 2+2 range-extended EV coupe added more fuel to the ”Why did they make the Volt a Chevy?” fire. As you certainly know, Cadillac has green-lighted a production version of the Converj, wisely renaming it the ELR in the process—although we’d still prefer a (properly spelled) real name to another bowl of alphabet soup. Since its production announcement, wild and occasionally entertaining rumors have swirled around the car ranging from “It’ll be just a re-skinned Volt” to “They’re going to put a big turbocharged four-cylinder in it.” It’s time to clear the air about the ELR.

The ELR Needs More—Everywhere—than the Volt

Although there are those who complain Chevy’s range-extended five-door hatchback sells for something resembling Caddy money, it is true that the Volt doesn’t play in Cadillac’s league when it comes to interior appointments and vehicle refinement. Adding refinement to the car to create a Cadillac-worthy model, however, also will add more of efficiency’s biggest enemy: weight. First, the car will get more sound-deadening materials—the ELR has to be properly Cadillac quiet, after all—and active engine mounts could be employed to tame gas-engine vibrations. GM also is considering other measures, such as better hood sealing, a coating on the firewall, and better firewall-passthrough gaskets to keep noise from the gasoline range-extender to an absolute minimum. There will be, naturally, a plethora of cosseting luxury appointments, which will add mass, too. (For reference, the Volt weighs 3766 pounds.)

Piling on pounds means that one of the largest ELR engineering challenges is finding a way to avoid making it feel like a slug while keeping it efficient. The adoption of a larger-displacement or turbo engine in place of the Volt’s 1.4-liter range-extender could raise the car’s performance some when the batteries are depleted, both to recharge them more quickly and in the case when the engine is driving the wheels directly. Taking full advantage of the extra juice from a more-powerful gas engine would almost certainly require the fitment of more-powerful electric motors. Unfortunately, a new engine likely will add even more weight, if only a marginal amount. Combined with all of the above pound-packing additions, that could have a disastrous effect on the ELR’s electric range and MPGe rating. (The 2012 Volt is rated for 94 MPGe combined and a 35-mile electric range. We’ve achieved 74 MPGe in a Volt and high 20s to mid-30s in terms of range, depending on conditions and driving style.)

Chevrolet Volt battery

Such a drop in efficiency could only be offset by increasing the storage capacity of the drive batteries. One of the changes for the 2013 Volt is a bump in total electrical storage capacity from 16.0 kWh to 16.5 kWh. While that might not sound like much of an increase, every tenth of a kilowatt-hour counts. One way for the heavier ELR’s pure-electric range to match that of the Volt would be to add more prismatic lithium-ion cells to the battery pack. On the downside, more storage capacity could mean more time to fully charge and the need for (at least slightly) increased battery-pack cooling capacity. And unless a new battery formulation is used, a higher-capacity battery means—you guessed it—more weight.

All of which illuminates a downside to the Voltec system in its current form: It doesn’t scale up very well. That’s one reason we haven’t seen GM spread the high-tech drive system around the company like peanut butter on hot toast—there’s a narrow weight/size matrix within which it works best. The system breaks down to four subsystems: drive motor-generator unit, power/control electronics, battery pack, and cooling. As vehicle size increases, the engine and battery subsystems have to grow in order to provide the same levels of performance and economy as the baseline. But as these two components increase in size and power, their cooling requirements also increase. More thermal management loads mean a higher-capacity cooling system and even more weight to cart around.

Chevrolet Voltec drive unit

Bit More of Everything to Maintain Performance

What we’re hearing is that the production ELR will swap the Volt’s 1.4-liter four for a naturally aspirated variant of the new Opel-developed Ecotec MGE. This all-new powerplant is the architectural base for a future family of low-emissions, direct-injection four-cylinders that will eventually replace most of GM’s Family 1 engines. Although the exact displacement of the ELR’s version is not known at this time, the block has been engineered to expand to as much as 2.0 liters. We’d expect to see the final version in the Caddy displace 1.8 liters at most, however. In order to keep the ELR’s pure electric range at least at the level of the Volt, battery capacity will be increased to more than 17.0 kWh; this will be accomplished by increasing the pack’s length and adding cells. Expect the “T” configuration of the pack to carry over. The Volt’s 4ET50 continuously variable transmission/drive unit will be revised to match its power output and electrical generation capacity to the new engine.

As the Cadillac will retail for a higher price than the Chevy, it will be able to absorb more cost; the ELR should then incorporate more lightweight, premium-cost materials. We therefore expect the ELR to weigh somewhere between 3850 and 3950 pounds—or about 100 more than the Volt—in spite of the heavier battery pack and ancillary systems. As to that price: This is a Cadillac, and it will carry a Cadillac sticker. Trading on the car’s green and style cred, don’t be surprised to see the small coupe landing with an MSRP in the mid-$50K range. For reference, that’s about $15,000 more than a base CTS coupe.

The ELR will not be Voltec’s last stand: There will be other applications for its more-powerful drive system. First up should be the rumored range-extended MPV/crossover, which is likely to wear a Buick badge.